This invention relates to a method of producing fiber-reinforced metallic building components, i.e. structural components, with a complicated three-dimensional geometry.
The extraordinary strength properties of SiC fibers are known. These properties in combination with their thermal stability has predestined ceramic SiC fibers for use as reinforcing elements for metallic materials. With regard to an intimate, load-transferring connection between the ceramic fibers and the metallic matrix, the fiber must first be provided with a well-adhering surface coating of a metal that is identical or at least xe2x80x9crelatedxe2x80x9d to the material of the building component from the standpoint of the subsequent diffusion bonding or diffusion welding. The fiber coating is usually provided by the PVD method, specifically by magnetron sputtering. The fiber-reinforced metallic building components ultimately produced are also known as MMCs (metal matrix composites). SiC fibers are produced as long fibers or continuous fibers with lengths of up to approximately 40 km, but fractions or sections 150 meters in length, for example, are usually used in construction practice. A preferred fiber diameter is approximately 100 xcexcm. A certain disadvantage of the rigid SiC fiber is its susceptibility to kinking, which is why it can be bent only with a relatively large radius of bending. The minimum bending radius for said 100 xcexcn fibers is approximately 2.5 cm. Due to the great length of the fiber, it is possible to apply it to building components that are to be reinforced by the winding technique to advantage, of course taking into account the fiber-specific minimum bending radius. Concrete applications so far have been mainly relatively simple rotor elements, e.g., in the form of rotationally symmetrical shafts, disks and rings or combinations of these elements. They should usually be produced by winding a metal-coated SiC long fiber around metallic carriers having a contour that corresponds at least mostly to the final form, covering the fiber windings with the metal, and producing a bonded monolithic structure, i.e., consolidating the resulting prefabricated unit in vacuo under the influence of pressure and temperature, the latter preferably by the HIP method (hot isostatic pressing). In addition to contoured components such as covers, sleeves, pipes, disks, etc., flexible and free-flowing elements such as films, wires, powders and the like may also be used as the covering for the fibers. Because of the favorable strength/weight ratio, titanium and its alloys have a preferred position among the materials to be reinforced. In this regard, see German Patent 4,324,755, for example.
For higher use temperatures, metals such as nickel and cobalt are recommended as matrix materials. Because of the great strength of the SiC fiber and its relatively low density (approx. 3.9 g/cm3) SiC-fiber-reinforced building components practically always permit lighter constructions than corresponding building components made only of metal. This again predestines MMCs with SiC reinforcement for use in high-speed rotors of all types. The fiber content that is currently feasible in the area of reinforcement is approx. 40 vol %.
The problem of production of MMC building components with SiC fiber reinforcement in complex, three-dimensional geometric shapes, e.g., in the form of blades for motors, has not been solved satisfactorily so far. First, it is practically impossible to cover a metal carrierxe2x80x94as a building component precursorxe2x80x94having a complex three-dimensional shape with the xe2x80x9cunmanageablexe2x80x9d SiC fibers in a defined manner, and definitely not by the preferred winding technique. On the other hand, consolidated SiC fibers, whose metallic surfaces have already formed bonds cannot be deformed permanently without destruction and/or breakage of the fibers.
Against this background, the object of this invention is to provide a method of producing SiC fiber-reinforced metallic building components which makes it possible to produce a defined fiber reinforcement in a reproducible and economical manner especially with the more complex three-dimensional geometric shapes, thus making the use of MMC technology for building components having complex shapes truly possible for the first time.
This object is achieved by process steps A through C characterized in Patent claim 1 in combination with the generic features in the introductory clause.
The above object has been achieved according to the invention in a method of producing a fiber-reinforced metallic building component or structural component. The principle of this invention is that metal-coated SiC fibers forming the fiber reinforcement are applied to a metallic sectional piece having a simple geometry and are held without being restrained thereon by means of a metallic counterpart piece, next the unit of the sectional piece, fibers and counterpart piece is plastically deformed and shaped into the complex final shape whereby the fibers are still xe2x80x9cloosexe2x80x9d and unbonded, and only then the unit is consolidated into a monolithic part by diffusion bonding. The steps of plastic deformation or shaping and consolidation take place at least mostly separately and in succession in the same device or within the same mold, with the process parameters of pressure, temperature and time being controlled appropriately. After consolidation, the part is still not a finished building component, so additional manufacturing steps such as cutting or joining must then follow.